Photodynamic therapy (PDT) is a developing therapy used for treatment of various cancers and also for non-malignant diseases including infections, wound-healing and various dermatological diseases. Photodynamic therapy is also used for cosmetic treatment of the skin. PDT involves the administration of a photosensitizer or a precursor thereof to an area of interest. The photosensitizer or precursor thereof is taken up into the cells, where a precursor of a photosensitizer is converted into a photosensitizer. Upon exposure of the area of interest to light, the photosensitizer is excited, usually from a ground singlet state to an excited singlet state. It then undergoes intersystem crossing to a longer-lived excited triplet state. One of the few chemical species present in tissue with a ground triplet state is molecular oxygen. When the photosensitizer and an oxygen molecule are in proximity, an energy transfer can take place that allows the photosensitizer to relax to its ground singlet state, and create an excited singlet state oxygen molecule. Singlet oxygen is a very aggressive chemical species and will very rapidly react with any nearby biomolecules. Ultimately, these destructive reactions will kill cells through apoptosis or necrosis, whereby for instance cancer cells are selectively killed. The mechanisms are still not fully understood, but studies suggest that the clinical result (i.e. the selectivity for cancerous cells) is not due to selective uptake by cancerous cells. Rather, there are similar levels of uptake in all cell types, but the processes of conversion and elimination are different in malignant cells and generally in metabolically active cells, such as inflamed or infected cells, leading to a concentration gradient between cancerous and normal tissue. Clinical experience has shown that PDT has advantages over alternative therapies for treatment of several pathological conditions; including acne, actinic keratosis and various skin cancers. A variation of PDT is PDT which is carried out without a photosensitizer or a precursor thereof, i.e. with light alone (also called phototherapy or light therapy).
U.S. Patent Application Publication No. 2011/0212146, which is incorporated herein in its entirety by reference hereto, describes the use of certain precursors of photosensitizers, i.e., derivatives of 5-aminolevulinic acid (5-ALA), such as for example, 5-ALA esters and salts thereof, in a method of cosmetic treatment of photoaged skin.
U.S. Patent Application Publication No. 2008/0188558, which is incorporated herein in its entirety by reference hereto, describes the use of certain precursors of photosensitizers, i.e., derivatives of 5-aminolevulinic acid (5-ALA), such as for example, 5-ALA esters and pharmaceutically acceptable salts thereof, in a method for photodynamic treatment of acne, e.g. acne vulgaris.
U.S. Patent Application Publication No. 2010/0137439, which is incorporated herein in its entirety by reference hereto, describes PDT, and in particular to the use of 5-aminolevulinic acid (5-ALA) and derivatives of 5-ALA in PDT, in which the side-effects (e.g. pain and/or erythema) of PDT, e.g. of PDT of acne, are prevented or reduced.
Acne is one of the most common human skin diseases, characterized by areas of skin with seborrhea (scaly red skin), comedones (blackheads and whiteheads), papules (pinheads), pustules (pimples), nodules (large papules) and possibly scarring. Acne affects mostly skin with the densest population of sebaceous follicles; these areas include the face, the upper part of the chest, and the back.
One element in safe and efficient PDT, e.g. photodynamic treatment of acne, is the light source, which may include lasers, conventional lamps, or lamps based on light emitting diodes (LEDs).
There are a number of advantages in using LEDs instead of conventional lamps or lasers for PDT. For example, an array of LEDs can be formed to cover a large area. In addition, their high efficiency ensures that less heat dissipation is necessary. Furthermore, LEDs have long term stability and so it is easier to design lamps which are suitable for tens of thousands of hours of operation.
U.S. Patent Application Publication No. 2004/0260365, which is incorporated herein in its entirety by reference hereto, describes a single panel photodynamic therapy lamp comprising a two-dimensional array of LEDs.
U.S. Patent Application Publication No. 2002/0029071 describes an arrangement of 4 panels of LED arrays comprising one panel for directing light to the scalp and 3 panels which are moveably connected to direct light onto the front of the face, the right side of the face and the left side of the face, respectively. Such a 4 panel LED lamp may be used for the treatment of the face and/or scalp, however, the arrangement of 4 panels makes the lamp fairly complex. A 4 panel LED lamp will also have a considerable weight, i.e. requiring suitable support arms and trolleys for moving the lamp. Due to its footprint, it will take up space in hospitals or private practice.
The photodynamic therapy lamps described in U.S. Patent Application Publication No. 2004/0260365 provide a limited treatment area. For example, when used for the photodynamic treatment of acne of a patient's face, as described in U.S. Patent Application Publication No. 2008/0188558, the lamp is not suitable to homogeneously illuminate the face in one illumination session and requires an operator to illuminate each side of the face individually. Likewise, when treating acne of a patient's chest or back, only a part of said chest or back can be treated in one illumination session. As a consequence, the side of the face or the part of the back or chest that is not presently undergoing treatment must be covered by appropriate means to prevent stray, unwanted illumination from impinging on such side or part. Therefore, the photodynamic therapy lamp requires a relatively long treatment time, additional operator functions, and additional materials in order to treat both sides of a patient's face or the entire chest or back. Moreover, the lamp must be precisely positioned independently for each side of the patient's face or each part of the patient's back or chest in order to ensure homogeneous illumination, thereby placing additional burdens on the operator to correctly perform the photodynamic treatment. Thus, in order to ensure correct treatment, the received light dose per side or part of the patient may need to be measured and evaluated, and subsequently, re-treatment of particular areas that did not receive the required light dose may be necessary, thereby further complicating and extending the treatment.
In order to treat a face of a patient suffering from acne, it is not sufficient to simply enlarge the lamps described in U.S. Patent Application Publication No. 2004/0260365 since although an enlarged lamp is able to illuminate the whole face in one illumination session, such an illumination is not homogeneous and thus it is not ensured that the correct light dose is administered to each part of the face.